Adhesive joint structure and adhesive joint structural components

Abstract

To provide an adhesion joint structure for maintaining adhesive strength when shearing force is applied, while aiming at a lower cost by reducing an amount used, capable of realizing by one kind of an adhesive agent, and also to provide a component having the adhesion joint structure.SOLUTION: An adhesion joint structure bonds a laminated adherent with an adhesive agent. When a direction to which shearing force is applied is a longer direction and a direction orthogonal to the direction to which the shearing force is applied is a width direction on an adhesion target surface of the adherent, at one end and the other end in the longer direction in an adhesion target region of the adherent, an adhesion joint structure includes: a pair of first adhesion portions with a length in the longer direction of shorter than 1 / 2 a total length of the adhesion target region and continuing across an entire width of the adhesion target region; and a second adhesion portion continuing in the longer direction, with a length in the width direction of shorter than the entire width of the adhesion target region, and connecting the pair of first adhesion portions.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an adhesive joint structure of joint members that are adhesively bonded by overlapping, and an adhesive joint structure component. In particular, in the automotive field, it relates to an adhesive structure suitable for strength members that require joint strength.

Background Art

[0002] From the perspective of environmental issues and towards the realization of carbon neutrality, vehicle weight reduction is being promoted in the automotive field. In recent years, due to the enrichment of driving assistance functions and the improvement of comfort, the vehicle body weight and cost tend to increase, so there is a need to achieve both further weight reduction and cost reduction. Among various efforts for weight reduction, multi-material is one of the keywords attracting attention. Multi-material is a technique for realizing weight reduction and performance improvement by combining and using different metals and materials, aiming to make the best use of various materials in the right place. The joining technology is important for making the best use of different materials. In addition to spot welding, which has been widely used in the past, laser welding, adhesive bonding, rivet bonding, bolt bonding, friction stir welding, etc. are adopted according to the application and material, and it is a field of technology development attracting attention.

[0003] Among these, adhesive bonding is being carried out in a wide range of fields due to its advantages such as being a lightweight method, being simple and easy to combine with other joining methods, etc., and research and development are being conducted to solve problems related to performance and reliability of adhesion, such as performance improvement, high functionality, or response to environmental changes.

[0004] Patent Document 1 presents a technique for obtaining high joint strength by applying a soft second adhesive to the adhesive end portion that becomes the fracture origin during shear stress loading in an overlapping adhesive joint.

[0005] Patent Document 2 presents a technique for overlapping adhesive joints in which a recess is provided in the adherend at the corner of the adhesive area. This increases the amount of adhesion at the corner of the adhesive area and at the interface between the adhesive and the adherend, where stress is concentrated when shear force is applied. By distributing this stress, interfacial failure is suppressed, cohesive failure of the adhesive is promoted, and stable high shear strength is obtained.

[0006] Patent Document 3 presents a technique for overlapping adhesive joints in which anchor particles are applied to the interface between the adhesive and the adherend to increase the strength of the adhesive interface, resulting in high adhesive strength and high adhesive strength reliability that can suppress the decrease in adhesive strength even when repeated stress is applied.

[0007] Patent Document 4 presents a technology for joining the outer and inner parts of the front pillar lower and the inner part of the side sill of an automobile. This technology involves applying adhesive in a vertical striped pattern along the shape of the mating flange surface, which is the adhesive joint, thereby ensuring rigidity with the minimum necessary amount of adhesive and achieving cost reduction by reducing the amount of adhesive used. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2020-180684 [Patent Document 2] Japanese Patent Publication No. 2017-1341 [Patent Document 3] Japanese Patent Publication No. 2018-69658 [Patent Document 4] Japanese Patent Publication No. 2009-1084 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, applying the above-mentioned conventional technology to the bonding of automotive steel sheets results in the following problems.

[0010] The technology described in Patent Document 1 presents cost challenges due to the increased amount of adhesive used, and production challenges such as increased maintenance and management of adhesives and increased complexity of the production process due to the need for a wider variety of adhesives. The technology described in Patent Document 2 requires a process of creating depressions on the surface of the adherend, which presents production and cost challenges due to increased man-hours. The technology described in Patent Document 3 presents cost challenges due to the increased material cost associated with the use of anchor particles. The technology described in Patent Document 4 concerns the optimization of the bonding position focusing on the rigidity of the joint. Compared to bonding the entire flange portion, it significantly reduces the amount of adhesive used, making it difficult to suppress the decrease in bonding strength.

[0011] The present invention was developed in view of the above-mentioned problems of the prior art, and its objective is to provide an adhesive joint structure and a component having the adhesive joint structure that can be implemented with one type of adhesive, aims to reduce costs by reducing the amount of adhesive used, while maintaining adhesive strength under shear load. [Means for solving the problem]

[0012] The adhesive joint structure according to the present invention, which advantageously solves the above problems, is configured as follows.

[0013] [1] An adhesive joint structure in which overlapping adherends are joined with an adhesive, wherein the direction in which a shear force is applied to the bonding surface of the adherends is the longitudinal direction, and the direction perpendicular to the direction in which the shear force is applied is the width direction, and the bonding area of ​​the adherends has a pair of first bonding portions in the longitudinal direction, one end and the other end, with a length in the longitudinal direction that is shorter than half the total length of the bonding area and continuous across the entire width of the bonding area, and a second bonding portion in the longitudinal direction, with a length in the width direction that is shorter than the entire width of the bonding area and connecting the pair of first bonding portions. [2] In the above [1], the second bonding portion is an adhesive joint structure comprising multiple portions, the sum of which is shorter than the total width of the area to be bonded. [3] In the above [1], the second adhesive portion is provided in pairs at both ends of the area to be bonded, and the sum of its widthwise lengths is shorter than the total width of the area to be bonded, forming an adhesive joint structure. [4] In the above [1] to [3], the adhesive joint structure is such that 55-90% of the area of ​​the adherend to be bonded is the bonded area.

[0014] The component having an adhesive joint structure according to the present invention, which advantageously solves the above problems, is configured as follows. [5] An adhesive joint structural component having the adhesive joint structure described in any one of the above items [1] to [4]. [Effects of the Invention]

[0015] According to the present invention, in an overlapping adhesive joint structure, it is possible to efficiently bond the adhesive area when shear force is applied, thereby maintaining adhesive strength while reducing the amount of adhesive used. Furthermore, while the main effect of reducing the amount of adhesive used is cost reduction, it also contributes to weight reduction, making it an effective measure against the recent trend of increasing vehicle weight and cost. Moreover, it can be implemented with a single type of adhesive, can be easily applied with existing adhesives, and does not complicate the process, so the impact on production is minimal, and it also has an advantage in terms of the cost of introducing the technology. [Brief explanation of the drawing]

[0016] [Figure 1] (a) is a schematic diagram showing the area to be bonded and the standard bonding range of the adherend, as well as the longitudinal and width directions of the adherend. (b) is a schematic diagram according to this embodiment showing a pair of widthwise continuous bonding portions (first bonding portions) and a pair of longitudinal continuous bonding portions (second bonding portions) connecting the first bonding portions at both ends in the longitudinal direction of the area to be bonded of the adherend. [Figure 2](a) is a schematic diagram showing the bonding site on the outer periphery of the bonding target area. (b) is a schematic diagram according to the present embodiment, having a pair of width-direction continuous bonding sites (first bonding sites) at both longitudinal ends of the bonding target area of the adherend, and a plurality of pairs of longitudinal-direction continuous bonding sites (second bonding sites) connecting the first bonding sites. (c) is a schematic diagram having a pair of width-direction continuous bonding sites (first bonding sites) at both longitudinal ends of the bonding target area of the adherend, and a longitudinal-direction continuous bonding site (second bonding site) connecting the first bonding sites only at one end in the width direction of the bonding target area. [Figure 3] It is an explanatory diagram of the tensile shear bond strength test method. [Figure 4] It is a graph showing the influence of the bonding area ratio (H-shaped and rectangular bonding sites) on the shear force by the tensile shear bond strength test. [Figure 5] It is a graph showing the influence of the bonding area ratio (outer periphery and rectangular bonding sites) on the shear force by the tensile shear bond strength test.

Mode for Carrying Out the Invention

[0017] Hereinafter, the adhesive joint structure according to the present embodiment will be described. The adhesive joint structure according to the present embodiment has, in the bonding target area of the adherend, a pair of first bonding sites that are continuous over the entire width of the bonding target area, with the longitudinal lengths at one end and the other end in the longitudinal direction being shorter than half of the total length of the bonding target area, and a second bonding site that is longitudinally continuous and connects the pair of first bonding sites, with the widthwise length being shorter than the total width of the bonding target area.

[0018] FIG. 1 shows the bonding range in the adhesive joint structure according to an embodiment of the present invention. In FIG. 1(a), the shaded area indicates the bonding range (bonding site) in the bonding target area. This is a conventional example where the entire bonding target area is the bonding range, and this bonding range is referred to as the standard bonding range. In the conventional adhesive joint structure, the bonding range shown in FIG. 1(a) is adopted. Figure 1(b) shows an example of the adhesive application range in an adhesive joint structure according to this embodiment, which has widthwise continuous adhesive portions at both ends in the longitudinal direction of the area to be bonded, and further has a longitudinally continuous adhesive portion at the widthwise center of the area to be bonded, extending from one end to the other in the longitudinal direction. In this adhesive joint structure, the area to be bonded of the adherend has a pair of first adhesive portions at one end and the other end in the longitudinal direction, with a longitudinal length shorter than half the total length of the area to be bonded, and extending continuously across the entire width of the area to be bonded. Furthermore, it has a second adhesive portion that is longitudinally continuous, with a widthwise length shorter than the entire width of the area to be bonded, and connecting the pair of first adhesive portions. In this case, the adhesive area of ​​the adherend is H-shaped, with the longitudinal direction being the horizontal direction of the H when viewed from directly above the adherend. Here, the direction in which the shear force is applied on the adhesive surface of the adherend is defined as the longitudinal direction, and the direction perpendicular to the direction in which the shear force is applied is defined as the width direction.

[0019] Figures 2(a) to 2(c) show another example of the adhesive application area in the adhesive joint structure according to this embodiment, in which the number of longitudinally continuous adhesive portions (second adhesive portions) connecting the pair of first adhesive portions and the adhesive pattern of their adhesive positions are changed, based on a pair of widthwise continuous adhesive portions that are shorter in the longitudinal direction than half the total length of the area to be bonded and are continuous across the entire width of the area to be bonded. In the adhesive joint structure shown in Figure 2(a), the adhesive portion in the area to be bonded of the adherend is on the outer periphery of the area to be bonded, and when viewed from directly above the adherend, it is in the shape of a square. The adhesive joint structure in Figure 2(b) is an example in which there are multiple longitudinally continuous adhesive sections (second adhesive sections) connecting a pair of first adhesive sections, and the adhesive sections in the area to be bonded of the adherend are ladder-shaped when viewed from directly above the adherend. The adhesive joint structure in Figure 2(c) is an example in which the longitudinally continuous adhesive portion (second adhesive portion) connecting the pair of first adhesive portions is located only at one end in the width direction of the area to be bonded. <Assumptions regarding the shape of the area to be bonded> It should be noted that the bonding area, the first bonding site, and the second bonding site shown in Figures 1 and 2 are assumed to be rectangular in shape. However, the corners of these rectangular shapes may be rounded as appropriate, taking into consideration the adhesive application method and the required bonding strength. Figures 1 and 2(a) show examples in which the corners have been rounded.

[0020] <Area ratio of the bonded area> This paper explains the results of a tensile shear bond strength test, which investigated the effect of the bond area ratio on the maximum load. Figure 3 is a schematic diagram of the tensile shear bond strength test method. Among the overlapping areas of the adherends, the area indicated by reference numeral 3 is the area to be bonded. The adhesive is applied to the area to be bonded 3, and the two adherends 2 are placed on top of each other and bonded together. Then, using a tensile testing machine, the adherends 2 are pulled in the manner indicated by the arrows indicated by reference numeral 4, and the tensile stroke, maximum load, etc., are evaluated. In the test method shown in Figure 3, an example of a test material is used in which the area to be bonded is 12.5 mm in the longitudinal direction and 16.0 mm in the width direction. Here, the bonded area ratio refers to the ratio (%) of the area to which the adhesive is applied to the area to be bonded.

[0021] Table 1 shows the test results for adhesive application shapes, specifically when the adhesive is applied in a rectangular shape and when it is applied in an H-shape according to the present invention. In Table 1, No. 1 is the case where the adhesive is applied to the entire surface of the area to be bonded. For the other conditions where the bonded shape is rectangular, the width and longitudinal application length of the adhesive were varied so that the bonded area ratio would be the value shown in Table 1. For Nos. 2 to 5, when the bonded shape is H-shaped, the adhesive application length BL at the first bonding site and the adhesive application width BW at the second bonding site (see Figure 1(b) for BL and BW) were adjusted to be equal in length so that the bonded area ratio would be the value shown in Table 1.

[0022] Figure 4 shows the effect of the ratio of the bonding area to the maximum load in the tensile shear bonding strength test. The vertical axis of Figure 4, representing the maximum load ratio, is the ratio (%) of the maximum load under each condition, based on the maximum load under condition No. 1 (where the application shape is rectangular and the adhesive is applied to the entire surface of the area to be bonded). In Figure 4, the circles (〇) indicate the case where the adhesive is applied in a rectangular shape, and the black diamonds (◆) indicate the case where the adhesive is applied in an H-shape. From these results, it can be seen that, for the same bonding area ratio, the maximum load is higher when the adhesive is applied in an H-shape than when the adhesive is applied in a rectangular shape.

[0023] [Table 1]

[0024] Table 2 shows the test results for adhesive application shapes, specifically when the adhesive is applied in a rectangular shape and when it is applied in a square shape according to the present invention. In Table 2, No. 1 is the case where the adhesive is applied to the entire surface of the area to be bonded. For the other conditions where the bonded shape is rectangular, the width and longitudinal application length of the adhesive were varied so that the bonded area ratio was the value shown in Table 1. For Nos. 2 to 5, when the bonded shape is square, the adhesive application length BL at the first bonding site and the adhesive application width BW at the second bonding site (see Figure 1(b) for BL and BW) were adjusted to be equal in length so that the bonded area ratio is the value shown in Table 2.

[0025] Figure 5 shows the effect of the ratio of the bonding area to the maximum load in the tensile shear bonding strength test. The vertical axis of Figure 5, representing the maximum load ratio, is the ratio (%) of the maximum load under each condition, based on the maximum load under condition No. 1 (where the application shape is rectangular and the adhesive is applied to the entire surface of the area to be bonded). In Figure 5, the circles (〇) represent the case where the adhesive is applied in a rectangular shape, and the black squares (■) represent the case where the adhesive is applied in a square shape. These results show that, for the same bonding area ratio, the maximum load is higher when the adhesive is applied in a square shape than when it is applied in a rectangular shape.

[0026] [Table 2]

[0027] The smaller the area of ​​adhesion by the adhesive on the bonded area of ​​the adherend, the lower the absolute value of the adhesive strength (shear stress). Therefore, in order to maintain adhesive strength, it is preferable to allow a decrease in adhesive strength of up to 10% compared to when the adhesive is applied to the entire bonded area, and to set the area ratio of the bonded area to the bonded area to 55% or more. From the viewpoint of ensuring adhesive strength, the area ratio of the bonded area is more preferably 60% or more, and even more preferably 65% ​​or more.

[0028] If the adhesive is applied in an H-shape or a square shape, and the area ratio of the bonded area is 65% or more, it is considered that the strength will be approximately the same as that of a standard rectangular bonded area. To ensure cost reduction by reducing the amount of adhesive used by 10% or more, it is preferable to keep the bonding area of ​​the bonding site 90% or less of the standard bonding range (area to be bonded).

[0029] Furthermore, if there are extremely narrow areas in the adhesive application width at the bonding site, the load load may concentrate starting from those areas, potentially leading to premature fracture. Therefore, to ensure adhesive strength, it is preferable to apply the adhesive with a width of 1 mm or more.

[0030] In actual production methods for applying adhesives, for example, when applying with a robotic gun, it is preferable to apply the adhesive in a predetermined shape by extruding it with a tip nozzle shaped to a predetermined application shape (H-shape), or by drawing lines multiple times with a tip nozzle shaped like a normal pen tip.

[0031] In a method where the tip nozzle shape is set to a predetermined application shape and then extruded, various bonding ranges can be accommodated by changing the nozzle size. Furthermore, when the bonding range is wider, for example, when bonding the flange portion of a hat-shaped joint, or when the bonding range extends linearly, it is possible to divide the bonding range into multiple areas and apply the predetermined shape to each area, for example, by continuously stamping. Alternatively, when using a standard tip nozzle, it is possible to accommodate a wide bonding range by drawing the predetermined shape without constraints on shape or size. [Examples]

[0032] The effects of this embodiment will be described in detail below based on the examples, but the present invention is not limited to these examples. Steel plate used in the test The material is cold-rolled steel sheet with a strength level of 590 MPa (TS). Its thickness is 1.4 mm, its width is 16.0 mm, and the longitudinal length of the bonding area is 12.5 mm. Adhesion conditions The adhesive used is a one-component heat-curing epoxy adhesive (Cemedine Co., Ltd., model number EP138). The adhesive application thickness is 0.5 mm. Tensile shear bond strength test specimens were prepared with adhesive joint structures that matched the adhesive application areas shown in Figures 1(b) and 2(a). Specimen No. 1 is the example shown in Figure 1(b), with BL (thickness of the bonded area in the width direction) = 3.9 mm, BW (thickness of the bonded area in the longitudinal direction) = 3.9 mm, and a bonded area ratio of 72%. Specimen No. 2 is the example shown in Figure 2(a), with BL (thickness of the bonded area in the width direction) = 3.1 mm, BW (thickness of the bonded area in the longitudinal direction) = 3.1 mm, and a bonded area ratio of 69%. For comparison, test specimens were also prepared with a rectangular adhesive area of ​​100% (test specimen No. 3) and 70% (longitudinal adhesive length 8.8 mm, test specimen No. 4).

[0033] For each test specimen, a tensile shear bond strength test was performed as shown in Figure 3, and the maximum load was measured.

[0034] In the tensile shear bond strength test, the maximum loads were 4.5 kN for the H-shaped bond in Figure 1(b) of the inventive example (test piece No. 1), 4.4 kN for the square-shaped bond in Figure 2(a) of the inventive example (test piece No. 2), 4.4 kN for the 100% rectangular bond in the comparative example (test piece No. 3), and 4.0 kN for the 70% rectangular bond in the comparative example (test piece No. 4). Therefore, for the same bonding area ratio, the H-shaped and square-shaped bonding methods had higher maximum loads than the rectangular bonding method, and the maximum shear stress load was at the same level as that of 100% rectangular bonding. [Explanation of Symbols]

[0035] 1. Method for testing tensile shear bond strength 2 Adherent material 3. Area to be bonded 4. Tensile load

Claims

1. In an adhesive joint structure in which overlapping adherends are joined with an adhesive, On the surface to be bonded to the adherend, The area to be bonded to the adherend is rectangular in shape or rectangular with rounded corners, The direction in which shear force is applied is the longitudinal direction. The direction perpendicular to the direction in which the shear force is applied is the width direction. year, The longitudinal length is 12.5 mm and the width is 16.0 mm, and the area to be bonded to the adherend is, A pair of first adhesive portions are provided at one end and the other end in the longitudinal direction, with a longitudinal length of 1 mm or more and shorter than half the total length of the area to be bonded, and continuous across the entire width of the area to be bonded, A second adhesive portion that is continuous in the longitudinal direction and connects the pair of first adhesive portions, having a length of 1 mm or more in the width direction and being shorter than the total width of the area to be bonded, It has, An adhesive joint structure in which 55-90% of the area to be bonded of the adherend is the bonding site.

2. The second bonding portion consists of multiple parts, and the sum of their widthwise lengths is shorter than the total width of the bonding target area. The adhesive joint structure according to claim 1.

3. The second adhesive portion is provided in a pair at both ends of the area to be bonded, and the sum of its widthwise lengths is shorter than the total width of the area to be bonded. The adhesive joint structure according to claim 1.

4. An adhesive joint structural component having the adhesive joint structure according to any one of claims 1 to 3.

Images